The invention relates to lightweight, interchangeable coupling devices used to join stringers at various angles on a common plane. The prior art teaches three basic concepts: contoured plates, U-shaped elements interconnected by pivots, and single piece molded units with slots. Contoured plates join stringers at common joints using two types of configurations. The first secures ends of stringers between two plates that are fastened together, and have preformed recesses. The second configuration uses band clamps to secure stringers to a single plate having preformed recesses. These plates do not allow interchanging of different size stringers, or use in applications which require different angles between the stringers; in addition, they are not conducive to fabrication from fiber-epoxy resin materials.
U-shaped elements secured to ends of stringers with their open ends interconnected by pivots are capable of holding stringers on a common plane, and being set at various angles. Rifken (U.S. Pat. No. 3,315,994) uses the U-shaped elements in conjunction with wedges attached to pivots that secure the stringers; such structures are not effective when the stringers are held at obtuse angles. The U-shaped elements are not desirable connector devices because wedges and pivots increase weight, and the U-shaped elements can only join stringers of similar diameters.
Single piece molded units with slots also exhibit undesirable characteristics because they only join stringers of predetermined shape at preset angles, and have excess material which increases weight.
Lightweight, universal coupling devices that join stringers of different shapes at various angles on a common plane are not taught by the prior art. In addition, existing coupling devices are not conducive to fabrication from unidirectional plies or warp/weft fabrics embedded in a resin, so special preparation of surfaces is necessary when joining stringers fabricated from lightweight, composite materials.
Accordingly, it is an object of this invention to provide a lightweight, universal connector which can be assembled at various angles to join stringers of different shapes on a common plane.
Another object of this invention is to provide gussets by joining the universal connectors with tabs extending therefrom.
Another object of this invention is to reduce weight and increase strength by alternately bonding the tabs, and trimming excess sharp corners.
Another object of the invention is to provide web elements to be used in conjunction with the universal connectors for forming tee-joints.
A prime object of this invention is to construct universial connectors of similar materials as fiber-resin stringers to eliminate problems with attaching the stringers to the connectors.
A further object of the invention is to construct structures 40% lighter than conventional steel and aluminum models by using unidirectional, composite materials embedded in a resin.